Zones in a wellbore have been isolated from each other with sand plugs. Typically, a porous substrate is supported in the wellbore and sand is pumped onto the substrate. Pressure is applied and the sand is dewatered. If a long enough sand column is created, the pressure applied from pumped fluid above forces the sand particles together in such a manner as to create a barrier to isolate zones in a wellbore from each other. When the barrier is no longer needed a jetting tool at the end of coiled tubing or the like is run into position above the plug. The jetting action and the circulation starts to work on the compacted sand pile and eventually allows the particles to come off the cohesive plug and get lifted from the well with the circulating fluid that exits the jetting nozzles. Some examples of this technique are U.S. Pat. Nos. 5,623,993 and 5,417,285. Other efforts in horizontal wells involve recipes of a variety of granular components that have predetermined properties such as specific gravity below 1.25 to create the plug using deposition techniques. One example of this is U.S. Pat. No. 7,690,427.
Other designs place swelling material in porous enclosures and allow the swelling action to create relative movement that allows a packer to go from a run in to a set position as overlapping petals of swelling material in enclosures rotate relatively to reach a sealing configuration in a borehole. This technique is illustrated in U.S. Pat. No. 7,422,071.
What is needed and provided by the present invention is a plug that can be set with a setting tool that creates relative movement and features a solid granular material in a porous enclosure where the setting action alters the shape of the enclosure to attain the set position. This can be done by bringing one end closer to another end and preferably through a passage in an annularly shaped sheath. Alternatively a swage can be brought through a passage in an annularly shaped sheath to enlarge the passage and in so doing set up the fill material in the sheath to push against the surrounding wellbore while a valve such as a flapper closes the passage to pressure from above. The porous enclosure can then be undermined in a variety of ways to allow the granular material to escape where it can be removed with fluid circulation. In some variations, a mandrel allows flow therethrough until an object is landed on a seat for zonal isolation. In other instances the mandrel can be undermined as a way of letting the granular material escape. The retaining porous material can be dissolved or in other ways removed so that it will not interfere with the working of other tools in the borehole. For fracturing plug purposes, perfect sealing is not required as long as sufficient flow past the plug is sufficiently slowed so that the acting pressure can deliver the requisite flow into the fractures to further open them, in the known manner. The use of a mandrel can also be optional and the plug structure can comprise a granular material in a porous enclosure that folds on itself to set. An optional lock feature or a valve to prevent reverse flow in the setting location when relative movement occurs can also be incorporated. These and other features can be incorporated into the design as will be more readily apparent to those skilled in the art from review of the details of the description of the preferred embodiment and the associated drawings, while understanding that the full scope of the invention is to be determined from the appended claims.